June 12, 2014 6:21pm EDTJune 12, 2014 4:49pm EDTCristiano Ronaldo set alarm bells ringing for Portugal on Thursday as he failed to complete his side’s training session and left the pitch in Campinas with a large ice pack on his left knee.Cristiano Ronaldo(AP Images)

Ben Hayward

Published on Jun. 12, 2014

Jun. 12, 2014

BELO HORIZONTE, Brazil -- Cristiano Ronaldo set alarm bells ringing for Portugal on Thursday as he failed to complete his side’s training session and left the pitch in Campinas with a large ice pack on his left knee.

The Real Madrid forward has been struggling with tendinosis but returned to action for 66 minutes in Portugal’s 5-1 friendly win over Ireland on Tuesday.

After that, the 29-year-old told reporters he was “99.9 percent fit,” but participated only in stretching with his teammates Thursday and left the pitch with an ice pack on his knee after signing autographs for fans.

Ronaldo then watched the rest of the session from the bench and his fitness remains a cause for concern ahead of Portugal’s World Cup opener against Germany in Salvador on Monday.

The Ballon d'Or winner has been hampered by injury problems since Real Madrid's Champions League final win over Atletico Madrid last month.